Endocrine Abstracts

Introduction: The short synacthen test (SST) is used in clinical practice to assess adrenal insufficiency (AI). However, the suggested threshold varies according to the patient cohort studied, assay variation and prevalence of the condition relative to the size of population tested. This study aimed to identify a threshold cortisol value to determine adrenal sufficiency in a Southeast Asian population and to investigate the utility of a stimulated 60-minute cortisol level in the diagnosis of AI.

Methods: We performed a retrospective analysis of 785 SSTs (250 micrograms) performed in our institution between 28 February 2022 to 28 February 2023. A normal response was defined as a stimulated cortisol value of ≥420 nmol/l at 30 or 60 min or at both time points, as measured by an Abbott Alinity Analyzer. Logistic regression analysis was performed to predict a normal response based on the baseline cortisol value.

Results: Median cortisol values at baseline, 30-min and 60-min after Synacthen stimulation were 254 (IQR 191–320) nmol/l, 499 (IQR 415–585) nmol/l, 574 (IQR 476–662) nmol/l respectively. Of the 785 SSTs, 83.0% of results were normal and 16.9% were abnormal. 55 SSTs (7.0%) would have been classified as AI if only the 30-min cortisol was assessed without the 60-min value, compared with 10 (1.4%) of patients would have failed using the 60-min cortisol without the 30-min value. An early morning basal cortisol (0800 h to 1200 h) cut-off value of <300 nmol/l identified a subnormal cortisol with 95% sensitivity and an afternoon cortisol (1200 h to 1700 h) of <312 nmol/l achieved 95.2% sensitivity. A basal cortisol level of <100 nmol/l will confirm AI with 97.3% specificity. Using a basal cortisol level of ≥300 nmol/l, 94.8% of individuals go on to pass the SST. Use of this basal cortisol value would have avoided 252 (32.1%) SSTs.

Conclusion: A single measurement of basal cortisol of ≥300 nmol/l, measured on the Abbott Alinity platform, has the potential to determine a normal response to an SST with 95% sensitivity on in our cohort of patients. Using a threshold cortisol level of 300 nmol/l, at least 32% of the SSTs could be avoided. Furthermore, a stimulated 60-min cortisol level identifies 55 (7%) of individuals who would otherwise be misclassified as AI. We believe this information may help clinician decide on situations where SST could be safely omitted, thus reducing unnecessary healthcare expenses.